Conventionally, computer systems providing large-scale data storage services to host computers have been provided. The computer systems are known to include a host computer, a storage system to which the host computer is coupled, and a management server of the storage system.
The storage system manages multiple hard disks via a RAID (Redundant Array of Independent/Inexpensive Disks) system. The storage system forms logical areas from physical storages areas included in the large number of hard disks and provides the same as logical volumes to the host computer. The host computer accesses the logical volume and sends read/write requests of data.
One example of such art for forming logical areas is called a capacity virtualization technique (a dynamic provisioning technique). According to the capacity virtualization technique, there is no physical storage area, and a logical volume having a virtualized storage capacity is assigned with respect to the host device. Such logical volume is called a virtual volume, and simultaneously when the host device requests a write access to the virtual volume, the storage system sequentially assigns storage areas to the virtual volume. Therefore, the present art enables to effectively utilize storage resources compared to a method in which a large capacity storage area is assigned from the beginning to the logical volume.
Patent literatures 1 and 2 are examples disclosing the capacity virtualization technique. In the method for assigning storage areas to a virtual volume according to the disclosed capacity virtualization technique, when a write access occurs from a host device to the virtual volume, a storage area from a capacity pool having a real storage area is assigned to the virtual volume address and the write data is stored therein. The storage area of the capacity pool is composed of a variety of memory media having various access performances and costs, wherein the frequently used data are stored in a storage area composed of memory media having a high access performance. This “capacity pool” (also simply referred to as “pool”) is formed for example by organizing multiple logic groups having real capacities to correspond to write requests to virtual volumes. The multiple logical volumes belonging to the pool are each referred to as pool volumes.
Further according to patent literature 2, whether the frequency of access to stored data is high or not is determined. If the access frequency is high, a media suitable for high speed processing is selected based on the physical characteristics information of the media (such as the media type or the rotation speed of disks) in the pool volume. Data is migrated to a pool of the pool volume composed of the selected media to improve the access performance thereof.